Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$98.37	5.581%	$103.86	$103.86	$103.85	$103.90
Purchase #2	$96.26	9.623%	$105.5231	$105.52	$105.50	$105.50
Purchase #3	$154.63	10.340%	$170.6187	$170.62	$170.60	$170.60
Purchase #4	$242.78	13.534%	$275.6378	$275.64	$275.65	$275.60
Purchase #5	$78.81	11.635%	$87.9795	$87.98	$88.00	$88.00
Purchase #6	$8.26	3.329%	$8.535	$8.54	$8.55	$8.50
Purchase #7	$69.38	13.244%	$78.5687	$78.57	$78.55	$78.60
7 purchase totals =	$748.49		$830.7228	$830.73	$830.70	$830.70